Lubricants in commercial use today are prepared from a variety of natural and synthetic base stocks admixed with various additive packages and solvents depending upon their intended application. Trends in automotive and industrial lubrication require formulations to achieve improved energy and fuel efficiency as well as greater stability. To achieve improved energy efficiency may require use of base stocks with lower viscosity, improved friction and lower traction. Although, at the same time, base stocks must also remain durable in increasingly severe conditions including high temperature and high workloads. Further, it is desirable that base stocks resist chemical degradation from common environmental elements, such as oxygen and water.
One category of base stocks, Group V base stocks, which are synthetic base stocks, find application in automotive and industrial lubricant formulations. Examples of Group V base stocks include esters, alkylated aromatics (e.g., alkylated naphthalenes), and polyalkylene glycols (PAGs). Group V base stocks are often incorporated into lubricant formulations to improve the solubility of additives, improve deposit performance, reduce volatility, and/or enhance the thermal-oxidative stability of the lubricant. However, it is difficult for a base stock to have a combination of such desirable properties. For example, esters are polar base stocks that help solubilize additives in hydrocarbon base stocks. However, esters may be susceptible to hydrolytic break down. Further, due to their high polarity, esters may interfere with an anti-wear additive's ability to interact with metal surfaces, thereby limiting esters' efficacies. Additionally, the polarity of esters can also cause incompatibilities with elastomer seals.
As another example, alkylated aromatics, particularly alkylated naphthalenes, have high oxidative stability. However, since alkylated naphthalenes are less polar than esters, they are not as capable as esters in solubilizing additives in the hydrocarbon base stocks. Furthermore, alkylated naphthalenes may have high pour points resulting in poor low temperature fluidity.
Therefore, there is a need for synthetic base stocks that can achieve a combination of desirable properties, including but not limited to: 1) improved low temperature fluidity, 2) low volatility, 3) high thermal-oxidative stability, and 4) low viscosity.